Production of sodium dichloroisocyanurate dihydrate

ABSTRACT

Anhydrous sodium dichloroisocyanurate is converted to the relatively stable dihydrate by controlled hydration under conditions which keep the temperature above freezing and not in excess of 40*C.

States Patent [1 1 EJite Berkowitz June 18, 1974 PRODUCTION OF SODIUM DICHLOROISOCYANURATE DIHYDRATE [75] Inventor: Sidney Berkowitz, Highland Park,

[73] Assignee: FMC Corporation, New York, NY.

[56] References Cited 7 UNITED STATES PATENTS 3,035,056 5/1962 Symes 260/248 Primary Examiner-John M. Ford [57] ABSTRACT Anhydrous sodium dichloroisocyanurate is converted to the relatively stable dihydrate by controlled hydration under conditions which keep the temperature above freezing and not in excess of 40C.

1 Claim, No Drawings PRODUCTION OF SODIUM DICHLOROISOCYANURATE DIHYDRATE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the production of sodium dichloroisocyanurate dihydrate from the anhydrous salt.

2. Prior Art The various dichloroisocyanurates are well-known materials which are widely used as a source of available chlorine in solid bleach and detergent compositions. Of these, the sodium salt is the most widely used. It is known to exist in the anhydrous form as the monohydrate (approximately 7.6 percent water of hydration by weight) and the dihydrate (14.1 percent combined water) see, for example, Symes US. Pat. Nos. 3,035,056 and 3,035,057 of May 15, 1962.

Most sodium dichloroisocyanurate is currently being sold in the anhydrous form. Despite the fact that the anhydrous salts are thermally stable to about 200C, when subjected to an intense source of heat, e.g., burning match, or cigarette butt, a progressive decomposition is initiated which results ultimately in destroying the entire mass. One method for handling this stability problem has been to include an inert filler with the salt to the extent of at least 30 percent by weight see, for example, Fuchs et al., US. Pat. No. 3,175,206. However, the inclusion of such large amounts of inert fillers is highly undesirable because of its additional handling,

shipping and packaging costs for substantial amounts of STATEMENT OF THE INVENTION I have discovered that conventional anhydrous or 1 partially hydrated sodium dichloroisocyanurate can be converted to a storage-stable product'which is mainly dihydrate by slowly adding the necessary amount of water to the solid anhydrous product while it is being agitated and cooled to a temperature above the freezing point, and not in excess of C, preferably no more than 40C.

When at least about 11 percent of water has been added (half dihydrate half monohydrate), the product is-sufficiently stable so that the material will not selfpropagate additional heat when subjected to a source of intense heat, such as a hot wire. More than minimal quantities of free moisture (that above 14.1 percent) should be avoided, as free moisture tends to react with the product.

DETAILED DESCRIPTION OF THE INVENTION Any solid commercial anhydrous sodium dichloroisocyanurate can be used in the practice of this invention, as well as partially hydrated material which is subject to progressive thermally initiated decomposition.

at a temperature below the decomposition point, can be used. The maximum temperature for safe operation is 50C; I prefer to operate at 40C or less. Any temperature above the freezing point of water is operable, although temperatures below ambient are uneconomic.

Typical of the apparatus which can be used to effect hydration is the Patterson-Kelly liquid-cooled Twin Shell Liquids-Solids Blender. I have also successfully used a fine spray of water'directed into a cooled ribbon blender in which the anhydrous material was being agitated, a rotating tray with air cooling, and a vibrating Sweco screen.

The dihydrate is quite stable at temperatures well above 50C, so that the temperature control can be eased once hydration is complete. However, it is generally convenient to maintain temperature control through most of the reaction period.

As indicated above, the product is hydrated to the point where it does not burn, i.e., where it contains at least about 1 1.0 percent of water. It may contain up to about 14.1 percent of water; more than a minor quantity of free water should be avoided.

EXAMPLES OF THE INVENTION Typical examples of the invention are given here by way of illustration, and not by way of limitation. All percentages are by weight unless otherwise specified.

Example 1 An 8 quart Patterson-Kelly Twin-Shell air-cooled Liquids-Solids Blender was charged with 2,268 grams of anhydrous granular sodium dichloroisocyanurate (20 mesh).

371 milliliters of water was added rapidly through an intensifier bar into the rotating material. The reaction temperature rose to45C. After the water addition was complete, blending was continued for an additional 30 minutes. The resultant dihydrate was a granular (-20 +70 mesh) odorless, free-flowing, dust-free material which assayed 55.2 percent available chlorine, theory 55.4 percent and 14.0 percent H O. X-ray diffraction patterns indicated the product to be essentially pure so dium dichloroisocyanurate dihydrate,

Example 2 Example 1 was repeated, hydrating to monohydrate, 11.0 percent water, and 12 percent water. The products were tested, along with the anhydrous material, by embedding an 18-gage nichrome wire in a 25 gram sample, and passing a current through the wire for several seconds, until the material in contact with the wire was decomposed. The current was then turned off.

The reaction in the anhydrous material and monohydrate continued to complete decomposition, rapidly. At 1 1 percent water, the reaction continued to completion, but very slowly; this seems the threshold value for safety. In the 12 percent and dihydrate samples, further decomposition stopped when the current was shut off.

roisocyanurate containing less than 1 1 percent by weight of water under such conditions that the temperature of the mix is maintained above the freezing point of water and not in excess of 50C, to obtain a product containing between 1 1 percent and 14.1 percent by weight of water of hydration. 

